In thin layer chromatography, sample plates are coated with a suitable "stationary phase" material such as a silica gel, for example. It is essential that this gel coating layer be uniform and continuous over the entire surface of the plate. The coated plates are subsequently placed in racks and the coating is allowed to dry. Once dried, the coated surface of the plate may be etched to form a plurality of narrow columns upon which sample analysis using chromatographic separation can be performed. A measured amount of a sample in its carrier, collectively identified as the "mobile phase", which may be a gas, liquid, or solid in solution, is introduced to the entry end of a column. The sample is then eluted using one or more solvents causing chemical separation along the column.
Some difficulty has been encountered in obtaining chromatographic plates of suitable quality. Manual application techniques typically result in 20 to 40% of the plates being discarded due to non-uniform coating. Such a non-uniform coating could effect the propagation rate of the sample along the column thereby affecting the outcome of the sample analysis. Until recently, satisfactory plates were available from a particular supplier. However, recent retirement of one or more of the supplier's key employees has resulted in degradation of the quality of plates available, thereby resulting in the experimentation that led to the present invention.
The present invention seeks to overcome the problems leading to the above-mentioned control difficulties. A plate holder for a glass sheet of sufficient length to form a plurality of chromatographic plates has lateral and longitudinal edge guides for positioning the plate. The plate holder further has a substantially smooth vertical surface along its upper edge. A guide bar on a liquid metering device engages the smooth vertical surface to guide the metering device and properly locate if relative to said chromatographic plates as it travels over the plates dispensing its coating. An adjustable doctor blade smooths out the coating uniformly over the surface of the plates. A motor draws the metering device along at a constant speed by means of a cable or cord to insure uniformity of the coating thickness. The motor preferably has a reostatic control associated with it so that the speed of movement of the metering device can be varied to suit the viscosity characteristics of the coating material being applied.
Various other features, advantages and characteristics of the apparatus of the present invention will become apparent after a reading of the following detailed description.